Mn/CeO2 CATALYST FOR DIMETHYL ETHER PRODUCTION VIA OXIDATIVE DEHYDRATION OF METHANOL

ABSTRACT

A method of producing dimethyl ether involving contacting methanol with a catalyst in the presence of oxygen in a reactor to form the dimethyl ether. The catalyst comprises manganese on a cerium oxide catalyst support, wherein a weight ratio of manganese to the cerium oxide catalyst support is in the range of 0.005 to 0.5. Further, a method of manufacturing the catalyst, including mixing cerium oxide (CeO 2 ) with a solution comprising manganese salt and a solvent, evaporating the solvent, followed by drying and calcining to form a catalyst which comprises manganese on a cerium oxide catalyst support, wherein a weight ratio of manganese to the cerium oxide catalyst support is in the range of 0.005 to 0.5.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to catalysts for producing dimethyl etherby oxidative dehydration of methanol.

DESCRIPTION OF THE RELATED ART

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Dimethyl ether (DME) has attracted attention as an additive for dieselfuel, because of its physical and chemical properties. DME has arelatively high cetane number and since a DME molecule does not containa C—C bond, very small amounts of soot are formed during a combustionprocess in a combustion engine. DME is a colorless and nontoxic compoundthat is in a liquid state at room temperature (20-30° C.) and elevatedpressure e.g. at least 7 bars. Accordingly, liquefied DME can be storedand transported like other liquid diesel fuels. In the liquid state, DMEmay be blended with Liquefied Petroleum Gas (LPG). DME can be used notonly as a diesel fuel but also as a mother liquor to produce manyvaluable chemicals. DME can be transformed into olefins, aromatics andother organic chemicals such as methyl acetate, formaldehyde andethanol. Thus, DME has diverse commercial uses. See W. Song, D. M.Marcus, H. Fu, J. O. Ehresmann, J. F. Haw, An Oft-Studied Reaction ThatMay Never Have Been: Direct Catalytic Conversion of Methanol or DimethylEther to Hydrocarbons on the Solid Acids HZSM-5 or HSAPO-34, Journal ofthe American Chemical Society, 124 (2002) 3844-3845; P. Cheung, A. Bhan,G. J. Sunley, E. Iglesia, Selective Carbonylation of Dimethyl Ether toMethyl Acetate Catalyzed by Acidic Zeolites, Angewandte ChemieInternational Edition, 45 (2006) 1617-1620; H. Liu, P. Cheung, E.Iglesia, Structure and support effects on the selective oxidation ofdimethyl ether to formaldehyde catalyzed by MoOx domains, Journal ofCatalysis, 217 (2003) 222-232; X. Li, X. San, Y. Zhang, T. Ichii, M.Meng, Y. Tan, N. Tsubaki, Direct Synthesis of Ethanol from DimethylEther and Syngas over Combined H-Mordenite and Cu/ZnO Catalysts,ChemSusChem, 3 (2010) 1192-1199, each incorporated herein by referencein their entirety. The size of the global market of DME is estimated tobe 3,740.46 kilo tons in 2014, and a compound average growth rate is15.67% in between 2015 and 2020. See Dimethyl Ether Market by RawMaterials (Coal, Methanol, Natural gas and Bio-based feedstock), byApplications (Aerosol Propellant, LPG Blending, Transportation fuel andOthers), and by Region—Trends & forecasts to 2020, in, 2015,incorporated herein by reference in its entirety. DME is mainlysynthesized by dehydration of methanol. Generally, acid catalysts (i.e.γ-alumina, zeolites etc.) are used for the dehydration reaction toproduce DME. See J. Sun, G. Yang, Y. Yoneyama, N. Tsubaki, CatalysisChemistry of Dimethyl Ether Synthesis, ACS Catalysis, 4 (2014)3346-3356, incorporated herein by reference in its entirety.

Reports indicate that acidic catalysts are used for the production ofDME from methanol via dehydration. Gamma-alumina (γ-Al₂O₃) has beenreported as the most promising catalyst because of its low cost, highDME selectivity, great thermal and mechanical stability. See S. S.Akarmazyan, P. Panagiotopoulou, A. Kambolis, C. Papadopoulou, D. I.Kondarides, Methanol dehydration to dimethylether over Al₂O₃ catalysts,Applied Catalysis B: Environmental, 145 (2014) 136-148 and D. Liu, C.Yao, J. Zhang, D. Fang, D. Chen, Catalytic dehydration of methanol todimethyl ether over modified γ-Al₂O₃ catalyst, Fuel, 90 (2011)1738-1742, each incorporated herein by reference in their entirety. Thereported performance of γ-Al₂O₃ is organized in Table 1. Zeolites (suchas HZSM-5, HY, HZSM-22 and H-SAPO) have strong acidic sites and alsobeen investigated as a potential catalyst for dehydration of methanol.See J. Fei, Z. Hou, B. Zhu, H. Lou, X. Zheng, Synthesis of dimethylether (DME) on modified HY zeolite and modified HY zeolite-supportedCu—Mn—Zn catalysts, Applied Catalysis A: General, 304 (2006) 49-54; D.Jin, B. Zhu, Z. Hou, J. Fei, H. Lou, X. Zheng, Dimethyl ether synthesisvia methanol and syngas over rare earth metals modified zeolite Y anddual Cu—Mn—Zn catalysts, Fuel, 86 (2007) 2707-2713; P. G. Moses, J. K.Norskov, Methanol to Dimethyl Ether over ZSM-22: A Periodic DensityFunctional Theory Study, ACS Catalysis, 3 (2013) 735-745; Q. Yang, M.Kong, Z. Fan, X. Meng, J. Fei, F.-S. Xiao, Aluminum Fluoride ModifiedHZSM-5 Zeolite with Superior Performance in Synthesis of Dimethyl Etherfrom Methanol, Energy & Fuels, 26 (2012) 4475-4480, each incorporatedherein by reference in its entirety. Unfortunately, in parallel with themain reaction, a formation of considerable amounts of byproducts such ashydrocarbons and coke takes place, resulting in deactivation of thecatalyst. In order to improve the activity and stability of the zeolite,it was mechanically mixed with CeO₂, but the addition of CeO₂ did notshow any positive effect. See D. Jin, B. Zhu, Z. Hou, J. Fei, H. Lou, X.Zheng, Dimethyl ether synthesis via methanol and syngas over rare earthmetals modified zeolite Y and dual Cu—Mn—Zn catalysts, Fuel, 86 (2007)2707-2713, incorporated herein by reference in its entirety.

TABLE 1 Catalytic activity and selectivity performance of the existingcatalysts Temp. Conversion Selectivity DME Catalyst (° C.) SV (%) (%)Ref. γ-Al₂O₃ 150-400 2500 (h⁻¹) 90 100 S. S. Akarmazyan, P.Panagiotopoulou, A. Kambolis, C. Papadopoulou, D. I. Kondarides,Methanol dehydration to dimethylether over Al2O3 catalysts, AppliedCatalysis B: Environmental, 145 (2014) 136-148. γ-Al₂O₃ 240-340 1 (h⁻¹)87 No info. D. Liu, C. Yao, J. Zhang, D. Fang, D. modified Chen,Catalytic dehydration of methanol to with Nb₂O₅ dimethyl ether overmodified γ-Al2O3 catalyst, Fuel, 90 (2011) 1738-1742. γ-Al₂O₃ 300 15600(h⁻¹) 86.4 100 F. Yaripour, F. Baghaei, I. Schmidt, J. modifiedPerregaard, Catalytic dehydration of with SiO₂ methanol to dimethylether (DME) over solid-acid catalysts, Catalysis Communications, 6(2005) 147-152. H—Y, and Fe—, 245 6000 (ml h⁻¹ g_(cat) ⁻¹) 86 No info.J. Fei, Z. Hou, B. Zhu, H. Lou, X. Zheng, Co—, Ni—, Synthesis ofdimethyl ether (DME) on Cr—, Zr— ion modified HY zeolite and modified HYexchanged Y zeolite-supported Cu—Mn—Zn catalysts, zeolite AppliedCatalysis A: General, 304 (2006) 49-54. H—Y zeolite 245 6000 (ml h⁻¹g_(cat) ⁻¹) 87.5 92.1 D. Jin, B. Zhu, Z. Hou, J. Fei, H. Lou, X. Zheng,Dimethyl ether synthesis via methanol and syngas over rare earth metalsmodified zeolite Y and dual Cu—Mn—Zn catalysts, Fuel, 86 (2007)2707-2713. CeO₂ mixed 245 6000 (ml h⁻¹ g_(cat) ⁻¹) 84.6 92.3 D. Jin, B.Zhu, Z. Hou, J. Fei, H. Lou, X. H—Yzeolite Zheng, Dimethyl ethersynthesis via methanol and syngas over rare earth metals modifiedzeolite Y and dual Cu—Mn—Zn catalysts, Fuel, 86 (2007) 2707-2713. TiO₂300 6.9 (mmol_(CH3OH) h⁻¹ g_(cat) ⁻¹) 4 84 R. Ladera, E. Finocchio, S.Rojas, G. Busca, J. L. G. Fierro, M. Ojeda, Supported WOx-basedcatalysts for methanol dehydration to dimethyl ether, Fuel, 113 (2013)1-9. WOx 300 6.9 (mmol_(CH3OH) h⁻¹ g_(cat) ⁻¹) 15 82 R. Ladera, E.Finocchio, S. Rojas, G. modified Busca, J. L. G. Fierro, M. Ojeda,Supported TiO₂ WOx-based catalysts for methanol dehydration to dimethylether, Fuel, 113 (2013) 1-9.

In view of the forgoing, a first objective of the present invention isto provide a method of manufacturing of a catalyst comprising manganese(Mn) supported on cerium oxide, and a second objective is to provide amethod of producing dimethyl ether by oxidative dehydration of methanol.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, the present disclosure relates to a methodfor producing dimethyl ether that involves contacting methanol with aMn/CeO₂ catalyst in a reactor to form the dimethyl ether. The catalystconsists of manganese supported on cerium oxide, wherein themanganese-cerium oxide catalyst has a weight percent ratio of manganeserelative to cerium oxide of 0.5% to 50%.

In one embodiment, the manganese-cerium oxide catalyst has a grain sizeof 0.05 mm to 0.5 mm.

In one embodiment, a temperature of the reactor is in the range of 275°C. to 450° C.

In one embodiment, a selectivity percentage for dimethyl ether from theconversion of methanol is in the range of 20-90 mol %.

In one embodiment, the catalyst is contacted with methanol in anoxygen/methanol mixture having a volume to volume ratio in the range of0.1 to 1.0.

In one embodiment, a selectivity percentage for dimethyl ether from theconversion of methanol is in the range of 20-90 mol %.

In one embodiment, a percentage yield of dimethyl ether, relative to amol % of the methanol converted, is 10 to 40% over a reaction time of 30hours to 90 hours.

In one embodiment, the prepared Mn/CeO₂ catalyst has surface area of 7m²/g-12 m²/g measured by Brunauer-Emmett-Teller (BET) method.

In one embodiment, the catalyst consists of a manganese-cerium oxide ina weight percent ratio of manganese relative to cerium oxide of 0.5% to50%.

According to a second aspect, the present disclosure relates to a methodof catalyst preparation. It includes mixing cerium oxide (CeO₂) with asolution comprising manganese salt and a solvent, evaporating thesolvent from the sludge to obtain solid residue of Mn/CeO₂, in form of apowder, drying at 110° C., calcining the solid residue at 90° C. to 500°C. for 5 h, sieving, granulating, and tableting.

In one embodiment, the solvent is water, ethanol, methanol,acetonitrile, or a combination thereof.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 shows XRD patterns of a CeO₂ catalyst, a 1% Mn/CeO₂ catalyst, a3% Mn/CeO₂ catalyst, and a 5% Mn/CeO₂ catalyst.

FIG. 2 is a graph depicting a methanol conversion and selectivitypercentiles with respect to hydrogen, carbon monoxide, carbon dioxide,formaldehyde, and dimethyl ether, for reactions in the presence of the1% Mn/CeO₂ catalyst, in the absence of an O₂ flow.

FIG. 3 is a graph depicting a methanol conversion and selectivitypercentiles with respect to hydrogen, carbon monoxide, carbon dioxide,formaldehyde, and dimethyl ether, for reactions in the presence of the1% Mn/CeO₂ catalyst, wherein a molar ratio of O₂ to methanol is 0.2.

FIG. 4 is a graph depicting a methanol conversion and selectivitypercentiles with respect to hydrogen, carbon monoxide, carbon dioxide,formaldehyde, and dimethyl ether, for reactions in the presence of the1% Mn/CeO₂ catalyst, wherein a molar ratio of O₂ to methanol is 0.2.

FIG. 5 is a graph depicting a methanol conversion and selectivitypercentiles with respect to hydrogen, carbon monoxide, carbon dioxide,formaldehyde, and dimethyl ether, for reactions in the presence of the1% Mn/CeO₂ catalyst, wherein a molar ratio of O₂ to methanol is 0.5.

FIG. 6 is a graph depicting a DME yield vs. temperature in the presenceof the 1% Mn/CeO₂ catalyst, wherein a molar ratio of O₂ to methanol is0, 0.2, 0.3, and 0.5.

FIG. 7 is a graph depicting a methanol conversion and selectivitypercentiles with respect to hydrogen, carbon monoxide, carbon dioxide,formaldehyde, and dimethyl ether, for reactions in the presence of the3% Mn/CeO₂ catalyst, wherein a molar ratio of O₂ to methanol is 0.5.

FIG. 8 is a graph depicting a methanol conversion and selectivitypercentiles with respect to hydrogen, carbon monoxide, carbon dioxide,formaldehyde, and dimethyl ether, for reactions in the presence of the5% Mn/CeO₂ catalyst, wherein a molar ratio of O₂ to methanol is 0.5.

FIG. 9 is a graph depicting a DME yield vs. temperature in the presenceof the 1% Mn/CeO₂, the 3% Mn/CeO₂, and the 5% Mn/CeO₂ catalysts.

FIG. 10 is a graph depicting data of a stability test of the 1% Mn/CeO₂catalyst.

FIG. 11 is a graph depicting data of a stability test of the 3% Mn/CeO₂catalyst.

FIG. 12 is a graph depicting methanol and oxygen conversions andselectivity percentiles with respect to hydrogen, carbon monoxide,carbon dioxide, formaldehyde, and dimethyl ether, for reactions in thepresence of the cerium oxide catalyst;

FIG. 13 is a graph depicting a DME yield vs. temperature in the presenceof the cerium oxide catalyst and the 1% Mn/CeO₂ catalyst.

FIG. 14 is a graph depicting methanol and oxygen conversions andselectivity percentiles with respect to hydrogen, carbon monoxide,carbon dioxide, formaldehyde, and dimethyl ether, for reactions in thepresence of a manganese oxide catalyst (i.e. MnOx).

FIG. 15 is a graph depicting a DME yield vs. temperature in the presenceof the manganese oxide catalyst and the 1% Mn/CeO₂ catalyst.

DETAILED DESCRIPTION OF THE EMBODIMENTS

According to a first aspect, the present disclosure relates to a methodfor producing dimethyl ether involving contacting methanol with acatalyst in a reactor to form the dimethyl ether (DME). The catalystcomprises manganese on a cerium oxide catalyst support. In someembodiments, the catalyst may include manganese oxide, manganese, orboth and cerium oxide.

Referring now to FIG. 1, in some embodiments, the catalyst includesmanganese and the cerium oxide catalyst support, wherein a weight ratioof manganese to the catalyst support is in the range of 0.005 to 0.5,preferably 0.01 to 0.3, preferably 0.01 to 0.1, preferably 0.01 to 0.05,preferably 0.02 to 0.05. FIG. 1 depicts an X-Ray diffraction pattern foran exemplary CeO₂ catalyst (FIG. 1-102), an exemplary 1 wt % Mn/CeO₂catalyst (FIG. 1-104), an exemplary 3 wt % Mn/CeO₂ catalyst (FIG.1-106), and an exemplary 5 wt % Mn/CeO₂ catalyst (FIG. 1-108).

The catalyst of manganese on a cerium oxide catalyst support may also bedenoted as “Mn/CeO₂” in this disclosure.

The term “catalyst support” refers to a solid substrate, whereinmanganese particles are deposited. The catalyst support may preferably aporous solid that provides a higher surface area for contactingmethanol, preferably in the presence of oxygen. Accordingly, in apreferred embodiment, the Mn/CeO₂ catalyst has a Brunauer-Emmett-Teller(BET) surface area in the range of 5 m²/g to 15 m²/g, preferably 6 m²/gto 14 m²/g, preferably 7 m²/g to 13 m²/g, preferably 7 m²/g to 12 m²/g.

The grain size of the Mn/CeO₂ catalyst might affect the rate and theselectivity of the oxidative dehydration reactions of methanol, due tothe diffusion limitations of methanol or reaction products. Therefore,in some embodiments, the Mn/CeO₂ catalyst are granulated and sieved toform catalyst grains with a grain size in the range of 0.05 mm to 0.5mm, preferably 0.75 mm to 0.4 mm, preferably 0.1 mm to 0.3 mm,preferably 0.2 mm to 0.25 mm.

In the oxidative dehydration of methanol to DME, side products may alsobe formed. In some embodiments, the side product may be hydrogen, carbonmonoxide, carbon dioxide, formaldehyde, or a combination thereof. Theformation of the side products is not an objective of the presentdisclosed catalyst or the method.

In a preferred embodiment, a selectivity of dimethyl ether from aconversion of 50 to 100 mol %, preferably 60 to 95 mol %, preferably 70to 90 mol % methanol is in the range of 20 to 100%, preferably 30 to95%, preferably 40 to 90%, preferably 50 to 85%, preferably 60 to 85%,preferably 65 to 80%. The term “selectivity” as used herein refers to apercentile of dimethyl ether produced in moles per moles of methanolconsumed. Furthermore, the term “conversion of methanol” refers to aratio (in percentile) of moles of methanol that is converted in areactor (i.e. an amount (in mole) of methanol that enters a reactorsubtracted by an amount (in mole) of methanol that exits the reactor),relative to the moles of methanol that enters the reactor. Thecalculations are further described in the Examples herein.

FIG. 2 represents a diagram of exemplary data of methanol contacting theMn/CeO₂ catalyst in the absence of an oxygen flow. The results depict alow conversion less than or equal to 20 mol %, preferably less than orequal to 10 mol %. A slight increase in the methanol conversion rate atelevated temperatures (i.e. above 350° C., preferably above 400° C.) isobserved.

An implementation of the presently disclosed method increases theconversion of methanol to dimethyl ether by contacting the catalyst witha mixture of methanol and oxygen. The mixture of methanol and oxygen hasa molar ratio of oxygen to methanol in the range of 0.1:1 to 1:1,preferably 0.1:1 to 0.6:1, preferably 0.2:1 to 0.6:1, preferably 0.2:1to 0.5:1. FIG. 3, FIG. 4, and FIG. 5 depict data from three exemplarycatalyst reaction tests of the catalyst having a 1% Mn/CeO₂, wherein amolar ratio of oxygen to methanol is 0.2:1, 0.3:1, and 0.5:1,respectively. In some embodiments, as shown in FIGS. 3, 4 and 5, 10 mol% to 50 mol %, preferably 10 mol % to 40 mol %, preferably 10 mol % to30 mol % of the methanol is converted to dimethyl ether or at least oneside product (hydrogen, carbon monoxide, carbon dioxide, andformaldehyde). Selectivity of dimethyl ether from the conversion ofmethanol may depend on the reaction temperature. Therefore, in allembodiments, a temperature of the reactor is in the range of 275° C. to450° C., preferably 275° C. to 400° C., preferably 275° C. to 350° C.Accordingly, the selectivity of dimethyl ether is in the range of 75 mol%-85 mol % or 80 mol % to 90 mol % in the temperature range between inthe range of 275° C. to 450° C., preferably 275° C. to 400° C.,preferably 275° C. to 350° C. in the presence of an O₂ flow. The sideproducts formed may be in the range of 0 to 20%, preferably 0 to 15%,more preferably 0 to 10% of the converted methanol in the above reactiontemperature ranges.

In one embodiment, 20 mol % to 100 mol %, preferably 30 mol % to 100 mol%, more preferably 40 mol % to 100 mol % of the oxygen is converted todimethyl ether or at least one of carbon monoxide, carbon dioxide,formaldehyde, and/or water.

In one embodiment, the catalyst remains stable during oxidativedehydration reactions in the reaction temperature of 275° C. to 450° C.,preferably 275° C. to 400° C., preferably 275° C. to 375° C., preferably300° C. to 375° C., for at least 50 hours, preferably at least 60 hours,preferably at least 65 hours, preferably at least 70 hours, preferablyat least 75 hours, preferably at least 80 hours, preferably at least 85hours, preferably at least 90 hours, preferably at least 95 hours,preferably at least 100 hours. The catalyst's stability may be measuredby a percent of deactivation. The term “deactivation” as used hereinrefers to a loss of catalytic activity (as a measure of reaction ratedecrease with time), which classifies as deactivation by type (chemical,thermal, and mechanical) and by mechanism (poisoning, fouling, thermaldegradation, vapor formation, vapor-solid and solid-solid reactions, andattrition/crushing). In one embodiment, a deactivation of the catalystis used to measure a stability of the catalyst during the oxidativedehydration reactions.

Referring now to FIG. 10 and FIG. 11, in one embodiment, no decrease inmethanol conversion and/or DME selectivity is detected in oxidativedehydration reactions over a period of at least 60 hours, preferably atleast 65 hours, preferably at least 70 hours, preferably at least 75hours, preferably at least 80 hours, preferably at least 85 hours,preferably at least 90 hours, preferably at least 95 hours, preferablyat least 100 hours, which indicates that the stability of the catalystin the reaction conditions, without any catalyst deactivation.

Further in some embodiments, the oxygen and methanol flow rate may bebetween 0.1 g/h to 0.7 g/h, preferably 0.2 g/h to 0.6 g/h, preferably0.3 g/h to 0.5 g/h. In some embodiments, methanol or the mixture ofmethanol and oxygen is mixed with helium with a volumetric ratio of 1:1to 1:9, preferably 1:2 to 1:6, preferably 1:3 to 1:4. In someembodiments, the methanol/helium or oxygen/methanol/helium gas mixtureshould be preheated prior to flowing into the reactor at a temperatureof 125° C. to 200° C., preferably 130° C. to 170° C., preferably 140° C.to 160° C. In some implementations, the oxygen/methanol/helium flow rateis in the range of 20 mL/min to 75 mL/min, preferably 30 mL/min to 60mL/min, preferably 40 mL/min to 50 mL/min. In some embodiments, a gashourly space velocity (GHSV) of the reactor is 10,000 cm³ h⁻¹ g_(cat) ⁻¹to 50,000 cm³ h⁻¹ g_(cat) ⁻¹, preferably 20,000 cm³ h⁻¹ g_(cat) ⁻¹ to40,000 cm³ h⁻¹ g_(cat) ⁻¹. Gas hourly space velocity relates the flowrate of the mixed gas and the weight of the catalyst, and GHSV ismeasured at standard temperature and pressure. In some embodiments, thecatalyst bed was preheated to a temperature from 200° C. to 300° C.,preferably 225° C. to 275° C., preferably 240° C. to 250° C. Thepreheated catalyst bed may be ramped to a reaction temperaturesimultaneously with the reactor temperature at a ramping rate of 1°C./min to 10° C./min, preferably 3° C./min to 8° C./min, preferably 5°C./min to 6° C./min. In some embodiments, the pressure of the reactor is0.5 atm to 1.5 atm, preferably 0.7 atm to 1.25 atm, more preferably 0.8atm to 1.0 atm.

The reactor may include, but is not limited to a fixed bed flow reactor,a moving bed reactor, or a fluidized bed reactor.

According to a second aspect, the present disclosure relates to a methodof manufacturing the Mn/CeO₂ catalyst including mixing cerium oxide(CeO₂) with a solution comprising a manganese salt and a solvent,evaporating the solvent to form a solid that includes manganese on acerium oxide catalyst support. The manganese salt may include but is notlimited to manganese bromide, manganese chloride, manganese carbonate,manganese fluoride, manganese iodide, manganese sulfate, and/ormanganese nitrate.

The term “mixing” as used herein preferably refers to a process thatincludes mechanical blending or agitation in a vessel by paddles, jets,or baffles. The mixing may occur sequentially or simultaneously. Forexample the manganese salt may first be dissolved or dispersed insolution, then followed by cerium oxide, or both manganese salt andcerium oxide may be combined in the solution simultaneously mixed. Insome implementations, the solvent in which the manganese salt and/or thecerium oxide is prepared by dispersion or dissolution may be water,ethanol, methanol, acetonitrile, or a combination thereof. In someimplementations, the solvent is at least 40% water, at least 30% water,at least 20% water, at least 10% water, or at least 1% water. In apreferred embodiment, the solvent is water and the manganese salt ismanganese chloride tetra hydrate (i.e. MnCl₂.4H₂O). In addition,evaporating may be accomplished by a vacuum evaporation, preferably arotary evaporation.

The method further involves drying the solid at a temperature of 90° C.to 120° C., preferably around 100° C. for 2 hours to 5 hours, preferablyabout 3 hours. Besides, the method involves calcining the solid at atemperature of 450° C. to 550° C., preferably around 500° C. for 3 hoursto 7 hours, preferably about 4 to 6 hours, more preferably about 5 hoursto form the catalyst.

In a preferred embodiment, the method further involves granulating thesolid to form catalyst grains in the size range of 0.05 mm and 0.5 mm,preferably 0.06 to 0.3 mm, preferably 0.07 to 0.2 mm, preferably 0.08 to0.1 mm.

In another preferred embodiment, the grains may further be sieved tocollect catalyst grains preferably with uniform shape and size. Thesieving may include high frequency vibrating equipment, which drives ascreen cloth to vibrate allowing material to be filtered that is smallerthan a pore size of the screen; gyratory equipment, which gyrates in acircular motion at a near level plane at low angles to cause a materialto shift back and forth and smaller material falls out of the box moreeasily than heavier material; or a trommel screens, which is ahorizontal rotating drum with screen panels around the diameter of thedrum through which material may be removed or captured based on size.

The examples below are intended to further illustrate the method ofproducing dimethyl ether and the method of manufacturing the catalystand are not intended to limit the scope of the claims.

Example 1

The dehydration of methanol to DME over γ-Al₂O₃ and zeolite catalysts iscarried out in the absence of oxygen whereas the present inventiondescribes a method to produce DME by oxidative dehydration of methanolover a catalyst composed of manganese supported on cerium oxide(Mn/CeO₂). The presently disclosed method employing the Mn/CeO₂ catalystrequires minimal oxygen presence in the reaction mixture in order toproduce DME from methanol with a high selectivity.

The presently disclosed catalyst, which comprises manganese supported onlow surface area CeO₂ demonstrates a high catalytic activity andselectivity in the reaction of oxidative dehydration of methanol to DME.The interaction between Mn and CeO₂ results in a change of the catalyticproperties of the CeO₂ as disclosed in data herein. Synergism wasobserved between deposited Mn and CeO₂, which causes an increase in thecatalyst efficiency towards producing the dimethyl ether. The result ofthis synergism was unexpected catalytic properties in the catalyst.Further, by combining a small amount of oxygen to the methanol feedstream, in the presence of Mn/CeO₂ catalyst, methanol was transformed toDME with high selectivity relative to side products. The proposedcatalyst composition for oxidative dehydration of methanol is differentfrom the conventional catalysts and process for DME production.

Example 2—Preparation of Mn/CeO₂ Catalyst

Manganese oxide was added to CeO₂ (Acros, Belgium, 99.9%) by incipientwetness impregnation method. To prepare 5 g of 1 wt % Mn supported onCeO₂ catalyst, 0.1876 g of Manganese Chloride Tetra Hydrate (MnCl₂.4H₂O,Techno Pharmchem HARYANA, India, 97%) was dissolved in 10 ml ofdeionized water at room temperature, resulting in a transparentsolution. 5 g of CeO₂ was then added to the MnCl₂ aqueous solution.Water was then evaporated by using a rotary evaporator having theoperating condition at 40° C. and 40-60 mbar. After completing theevaporation, the resulting powder was collected and dried in an oven at100° C. for 3 h. The powder was then calcined in static air at 500° C.for 5 h. The desired temperature was attained by increasing the oventemperature from 25° C. to 500° C. having a ramping rate of 5° C. min⁻¹.

The obtained powder material was tableted, and the tablets weregrounded. A fraction of the grounded material with grain size between0.08 and 0.1 mm was selected and used for catalytic activity andselectivity measurements. 3 wt % and 5 wt % Mn supported on CeO₂catalysts were also prepared by the same procedure as 1 wt % Mn/CeO₂catalyst.

All catalysts are characterized as follows. Crystal structure of theprepared catalysts was characterized by X-ray diffraction. FIG. 1 showsXRD patterns of 1% Mn/CeO₂, 3% Mn/CeO₂, 5% Mn/CeO₂ and pure CeO₂support.

Specific surface area of the catalysts was measured by using N₂adsorption isotherms and Brunauer-Emmett-Teller (BET) analysis. Beforethe nitrogen adsorption, all the catalysts were degassed at 200° C. for2 h under vacuum condition in order to remove adsorbates on thecatalysts. The values of the surface area are shown in Table 2.

TABLE 2 BET surface area of the catalysts Sample CeO₂ 1% Mn/ 3% Mn/ 5%Mn/ support CeO₂ CeO₂ CeO₂ Surface area (m²/g) 10.0 9.6 8.6 8.0

Composition of the catalysts was analyzed by X-ray Fluorescence (XRF) asshown in Table 3. The nominal values (wt %) of Mn content are very closeto the desired value of the preparation condition.

TABLE 3 Composition of the catalysts (wt %) 1% Mn/CeO₂ 3% Mn/CeO₂ 5%Mn/CeO₂ Ce 99.06 96.39 94.50 Mn 0.94 3.60 5.50

Example 3—Oxidative Dehydration of Methanol Over 1% Mn/CeO₂ Catalystswith Different O₂/MeOH Ratios

The process of the oxidative dehydration of methanol was carried out byusing (PID Eng & Tech, System, Spain) with a fixed bed quartz reactor atatmospheric pressure in the temperature interval between 275 and 450° C.The reactor was charged with 0.1 g of catalyst with grain sizes between0.08 to 0.1 mm. The catalyst bed was supported on the bed of quartzwool. The internal diameter of the quartz reactor was 4 mm, and theheight of the catalyst bed was 7-8 mm. A K-type thermocouple was placedat the center of the catalyst bed to measure the reaction temperature.

Liquid methanol flow was controlled by Bronkhorst High-Teck B.V. CEMsystem at 0.45 g h⁻¹. Oxygen (O₂) flow was controlled at O₂/MeOH ratioof 0.2, 0.3, and 0.5 (mol/mol) by a mass flow controller (BronkhorstHigh-Teck B.V.).

The required methanol and oxygen flow were mixed with helium in a mixingchamber heated at 150° C. The total flow of oxygen, methanol and inertHe was 50 ml/min, and gas hourly space velocity (GHSV) was 30,000 cm³h⁻¹ g_(cat) ⁻¹.

Catalyst bed was preheated to 250° C. prior to introduce the reactantsto the reactor. The reactor temperature was then increased to 275° C. ata ramping rate of 5° C./min. For each desired experimental condition,temperature (in between 275-450° C.) was held for 3 h to reach steadystate prior to analyze the reaction products. The reactants and productswere analyzed with an on-line gas chromatograph (HP, G1540A) equippedwith TCD detectors. Molecular sieve 13X was used to separate O₂ and CO,and Porapak QS was used to separate H₂, CO₂, H₂O, CH₂O (Formaldehyde),CH₃OH and CH₃OCH₃ (Dimethyl ether).

Conversion (%) of reactants and selectivity of products were calculatedas follows in equations (1)-(7).

$\begin{matrix}{{{CH}_{3}{OH}\mspace{14mu} {conversion}\mspace{14mu} (\%)} = {\frac{{{{mol}.\mspace{14mu} {of}}\mspace{14mu} {CH}_{3}{OH}_{in}} - {{{mol}.\mspace{14mu} {of}}\mspace{20mu} {CH}_{3}{OH}_{out}}}{{{mol}.\mspace{14mu} {of}}\mspace{14mu} {CH}_{3}{OH}_{in}} \times 100}} & (1) \\{{O_{2}\mspace{14mu} {conversion}\mspace{14mu} (\%)} = {\frac{{{{mol}.\mspace{14mu} {of}}\mspace{14mu} O_{2{in}}} - {{{mol}.\mspace{14mu} {of}}\mspace{20mu} O_{2{out}}}}{{{mol}.\mspace{14mu} {of}}\mspace{14mu} O_{2{in}}} \times 100}} & (2) \\{{{CH}_{2}O\mspace{14mu} {selectivity}\mspace{14mu} (\%)} = {\frac{{{mol}.\mspace{14mu} {of}}\mspace{14mu} {CH}_{2}O}{{{mol}.\mspace{14mu} {of}}\mspace{14mu} {CH}_{3}{OH}_{consumed}} \times 100}} & (3) \\{{{CO}\mspace{14mu} {selectivity}\mspace{14mu} (\%)} = {\frac{{{mol}.\mspace{14mu} {of}}\mspace{14mu} {CO}}{{{mol}.\mspace{14mu} {of}}\mspace{14mu} {CH}_{3}{OH}_{consumed}} \times 100}} & (4) \\{{{CO}_{2}\mspace{14mu} {selectivity}\mspace{14mu} (\%)} = {\frac{{{mol}.\mspace{14mu} {of}}\mspace{14mu} {CO}_{2}}{{{mol}.\mspace{14mu} {of}}\mspace{14mu} {CH}_{3}{OH}_{consumed}} \times 100}} & (5) \\{{{DME}\mspace{14mu} \left( {{CH}_{3}{OCH}_{3}} \right)\mspace{14mu} {selectivity}\mspace{14mu} (\%)} = {\frac{2\mspace{14mu} \left( {{{mol}.\mspace{14mu} {of}}\mspace{14mu} {CH}_{3}{OCH}_{3}} \right)}{{{mol}.\mspace{14mu} {of}}\mspace{14mu} {CH}_{3}{OH}_{consumed}} \times 100}} & (6) \\{{{DME}\mspace{14mu} {yield}\mspace{14mu} (\%)} = {{CH}_{3}{OH}\mspace{14mu} {conversion} \times {DME}\mspace{14mu} {{selectivity}/100}}} & (7)\end{matrix}$

FIG. 2, FIG. 3, FIG. 4 and FIG. 5 show MeOH conversion and selectivityobtained on 1% Mn/CeO₂ at O₂/MeOH ratio of 0, 0.2, 0.3 and 0.5,respectively. DME yields at each O₂/MeOH ratio were compared as shown inFIG. 6.

The 1% Mn/CeO₂ catalyst showed quite small activity at the conditionwithout O₂ flow as shown in FIG. 2 and FIG. 6. Conversion measurementsbelow 5% were a result of error in methanol flow rate. At thetemperature range between 275° C. and 375° C., a small amount of DME wasgenerated. When O₂ was supplied with methanol at O₂/MeOH ratio of 0.2,0.3 and 0.5, a considerable amount of methanol was reacted and DME wasobtained as main product at a temperature range between 275 and 325° C.DME yield was significantly increased with increase of the O₂ flow asshown in FIG. 6. These results suggest that DME production over Mn/CeO₂catalyst needs oxygen and follows a different mechanism compared to thedehydration mechanism on γ-Al₂O₃ and on zeolites. 300° C. is anadvantageous temperature because conversion at 300° C. is higher thanthat of 275° C. and DME selectivity at 300° C. is higher than that of at325° C. Higher O₂/MeOH ratio brought higher selectivity for CO₂,resulting in relatively lower DME selectivity. Therefore, it wasconcluded that the reaction temperature at 300° C. and the O₂/MeOH ratioat 0.2 for oxidative dehydration of methanol to DME, provided a usablelevel of DME yield.

Example 4—Oxidative Dehydration of Methanol Over Mn/CeO₂ Catalysts withDifferent Mn Contents

Activity of 3% Mn/CeO₂ and 5% Mn/CeO₂ was tested at O₂/Me ratio of 0.2,according to the same procedure as above in the preparation of Mn/CeO₂catalyst, as shown in FIG. 7 and FIG. 8. DME yields obtained overMn/CeO₂ catalysts with different Mn contents were compared as shown inFIG. 9. The increase of Mn content increases DME selectivity at middletemperature range (between 350 and 375° C.). However, at lowertemperature such as 275 and 300° C., Mn content hardly influenced theactivity and selectivity.

Example 5—Stability Test of 1% and 3% Mn/CeO₂ Catalysts at O₂/MeOH Ratioof 0.2

Methanol oxidative dehydration reaction over 1% and 3% Mn/CeO₂ wasisothermally performed at 300° C. and O₂/MeOH ratio of 0.2 in order toexamine the stability of the catalysts. As a result, both 1% Mn/CeO₂ and3% Mn/CeO₂ catalysts didn't show any significant deactivation or anydecrease in DME selectivity for a time period of 80 hours.

Example 6—Oxidative Dehydration of Methanol Over Manganese Oxide

Manganese oxide (MnOx) was synthesized by calcination of Manganesechloride (MnCl₂.4H₂O, Techno Pharmchem HARYANA, 97%) at 500° C. for 5 haccording to the same calcination condition to prepare Mn/CeO₂catalysts. The activity of 100 mg of the synthesized MnOx was examinedat O₂/MeOH ratio of 0.5 according to the same procedure as Mn/CeO₂catalysts. As a result, MnOx showed much lower activity and DME yield at300° C. than those of Mn/CeO₂ catalysts as shown in FIG. 14 and FIG. 15.In addition, DME selectivity is also lower than Mn/CeO₂ catalyst becauseof increased amount of formaldehyde production.

Example 7

The analysis of the composition of the reaction mixture at the reactoroutput were done by gas chromatographic method by using the followingchromatographic columns of a molecular sieve, Porapak®, Tenax®,hayeSep®, and Chromosorb.

FIG. 6 shows a comparison of data derived from FIG. 3, FIG. 4, and FIG.5. The highest selectivity for DME and higher conversion of methanolwere obtained at the reaction temperature of 300° C. and O₂/MeOH ratioof 0.2 as depicted in FIG. 3. FIG. 7 and FIG. 8 depict data fromexemplary reaction tests of 3% Mn/CeO₂ and 5% Mn/CeO₂ catalysts,respectively, at an oxygen/methanol ratio of 0.2. FIG. 9 depicts acomparison of data in FIG. 7 and FIG. 8.

FIG. 10 and FIG. 11 depict data from two stability tests over 80 hourseach. These stability tests demonstrated that Mn/CeO₂ catalysts don'tshow any significant deactivation on their methanol conversion andselectivity for DME.

FIG. 12 and FIG. 13 depict a comparison of a CeO₂ support's catalyticefficiency in forming DME as compared to a 1% Mn/CeO₂ catalyst'sefficiency in forming DME. As shown in FIG. 13, the yield of DME overCeO₂ is four to ten times smaller or five to eight times smaller thanthe yield obtained by using Mn/CeO₂ at 300° C. to 375° C. The comparisonclarifies that pure CeO₂ support does not efficiently catalyze the DMEproduction from methanol. Further, FIG. 14 and FIG. 15 depict dataresulting from DME formation with a catalyst comprising only manganeseoxide as compared to Mn/CeO₂. The data in FIG. 14 and FIG. 15 show thatpure manganese oxide does not exhibit any catalytic activity until atemperature of 325° C. When Mn is supported on CeO₂, the obtainedcatalyst produces DME at temperatures as low as 275° C. Taking the datadepicted in FIG. 13 and FIG. 15 together, the obtained figures areshowing a proof that between Mn and CeO₂ arises synergetic effect, thatis exploited by the catalyst disclosed in the present invention and themethod of producing DME as described herein. The yield of DME overMn/CeO₂ at temperatures of 275° C. to 375° C. is two to five timesgreater than expected DME yield obtained by sum DME yields of pure CeO₂and manganese oxide, which have no synergetic effect.

DME yields obtained at 300° C. and various O₂/MeOH ratios over CeO₂,MnOx and Mn/CeO₂ catalysts are organized in Table 4. The results clearlysuggest that a synergistic effect between manganese oxide and ceriaoxide significantly improves the catalytic activity to produce DME frommethanol. The data suggests that O₂ improves the production of DME withan Mn/CeO₂ catalyst.

TABLE 4 DME yields obtained at 300° C. and various O₂/MeOH ratio. DMEYield DME Selectivity Sample O₂/MeOH (%) (%) CeO₂ 0.5 3.2 — MnOx 0.5 0.7— 1% Mn/CeO₂ 0 5.0 — 0.5 20.1 83 0.3 16.8 85 0.2 19.2 86 3% Mn/CeO₂ 0.214.4 78 5% Mn/CeO₂ 0.2 17.6 84

Presented herein is a catalyst to produce DME from Methanol withaddition of oxygen; a synergistic effect between manganese oxide andcerium oxide has an important role for the reaction; Oxygen with themethanol may efficiently produce DME. The catalyst showed a highstability. 1% Mn/CeO₂ and 3% Mn/CeO₂ did not show any significantdeactivation or decrease of DME selectivity during reaction carried outfor longer than 60 h at 300° C. Oxygen may be included in the reactantstream to produce DME.

1: A method of producing dimethyl ether comprising: contacting a mixtureof methanol and oxygen with a catalyst in a reactor to form the dimethylether via oxidative dehydration of methanol, wherein the catalystcomprises manganese on a cerium oxide catalyst support, wherein a weightratio of manganese to the cerium oxide catalyst support is in the rangeof 0.005 to 0.5. 2: The method of claim 1, wherein the reactor is afixed bed reactor. 3: The method of claim 1, wherein 1 to 20 mol % ofthe methanol is converted to dimethyl ether. 4: The method of claim 1,wherein methanol and oxygen are contacted with the catalyst at atemperature in the range of 275° C. to 450° C. 5: The method of claim 1,wherein a selectivity of dimethyl ether from a conversion of 50 to 100mol % methanol is in the range of 20 to 100%. 6: The method of claim 1,wherein a molar ratio of oxygen to methanol in the mixture of methanoland oxygen is in the range of 0.1:1 to 1:1. 7: The method of claim 1,wherein 20 to 100 mol % of the oxygen is converted to dimethyl ether. 8:A method of manufacturing the catalyst of claim 1, comprising: mixingcerium oxide with a solution comprising manganese salt and a solvent;evaporating the solvent to form a solid; drying and calcining the solidat a temperature in the range of 100 to 500° C. to form the catalyst,which comprises manganese on a cerium oxide catalyst support, wherein aweight ratio of manganese to the cerium oxide catalyst support is in therange of 0.005 to 0.5. 9: The method of claim 8, further comprising:granulating the catalyst to form catalyst grains with a grain size inthe range of 0.05 mm to 0.5 mm. 10: The method of claim 1, wherein thecatalyst comprises the manganese on a solid porous cerium oxide catalystsupport. 11: The method of claim 1, wherein the catalyst consistsessentially of manganese and the cerium oxide catalyst support. 12: Themethod of claim 1, wherein the catalyst does not comprise a zeolite. 13:The method of claim 1, wherein the catalyst has an X-ray diffractionpattern with a main peak for CeO₂. 14: The method of claim 1, whereinthe catalyst consists of the manganese and the cerium oxide catalystsupport. 15: The method of claim 1, wherein 1 to 50 mol % of themethanol is converted to dimethyl ether. 16: The method of claim 1,wherein the catalyst comprises the manganese as the only active metal ona solid porous cerium oxide catalyst support.